Field test in Qinghai shows Back Contact solar modules outperform TOPCon by over 3%

A recent field test conducted at a residential complex in Qinghai, China, offers new insights into how back contact (BC) solar modules compare to the widely adopted TOPCon technology. The results add weight to the argument that BC is not only a contender but may be the front-runner for the next generation of high-efficiency solar modules.

The test site, located in Xining at 2,327 meters altitude and characterized by a semi-arid plateau climate with around 2,500 sunshine hours annually, was set up to allow real-world performance comparison. Modules were installed on a fixed-tilt system (10° inclination) to simulate flat rooftops (especially commercial or industrial buildings) and ground-mounted systems in high-sun regions, optimized for midday sun and wind resistance.

The comparison involved LONGi's HPBC 2.0 Hi-MO 9 modules, each with 650W output and a total capacity of 11.7 kW, versus a set of TOPCon modules with slightly lower output (610W) but greater total capacity (49.8 kW). Both had identical dimensions (2382 × 1134 mm), allowing a direct apples-to-apples evaluation on a per-kilowatt basis.

BC advantage confirmed in monthly output

In April, BC modules delivered 288.21 kilowatt-hours per kilowatt (kWh/kW), outperforming the TOPCon reference, which achieved 279.95 kWh/kW. That’s a 2.95% gain in energy generation, an improvement that can translate into substantial lifetime gains for businesses installing BC modules.

Weather-based analysis shows consistent gains

The data becomes even more compelling when broken down by weather conditions. On April 14, an overcast day, BC modules showed a 3.16% higher output than TOPCon. Analysis using 5-minute interval data revealed that BC modules responded better in low-light conditions: they began generating electricity earlier in the morning and sustained higher output throughout periods of reduced irradiance.

On April 12, a clear sunny day, BC modules still maintained a 2.82% generation edge. Once again, they exhibited an earlier morning startup, showing that BC’s performance advantage is not limited to one specific weather type.

Back contact technology and LONGi’s TaiRay wafer enabler of results

The performance difference is tied to the design of LONGi’s HPBC 2.0 modules. These integrate proprietary TaiRay silicon wafers which are known for their high-performance and mechanical resistance. They are engineered with enhanced impurity removal capabilities, facilitating higher cell efficiencies across various photovoltaic technologies such as heterojunction (HJT), and back-contact (BC) cells. This in turn enhances light absorption and power conversion, particularly under weak or variable sunlight, providing a clear technical advantage over the gridlined surface of TOPCon modules.

White Paper validates BC as the next mainstream PV technology

These field results align with findings from the recent industry white paper presented at Intersolar 2025, co-authored by LONGi, Aiko Solar, TÜV Rheinland, the China Electricity Council, and the China General Certification Center. The white paper identifies back contact (BC) technology as the leading candidate to drive the next era of photovoltaic innovation. It highlights that BC solar cells can deliver up to 11% more energy over their lifecycle compared to TOPCon modules, thanks to improved light absorption and the elimination of front-side metal wiring. Additionally, BC modules have demonstrated up to 33% higher energy generation in shaded conditions. The report also notes that advancements in BC manufacturing have reduced equipment investment costs by over 60% and increased production capacity fivefold, making BC technology both high-performing and cost-competitive. The full report can be viewed here: short.longi.com/back-contact-whitepaper

Qinghai field data reinforces back contact as front-runner for next-gen solar efficiency

While the test site is just one of many ongoing pilot locations, the findings acknowledge that back contact technologies are increasingly proving their real-world superiority. For energy system designers, installers, and end users in regions with variable weather or morning/evening self-consumption peaks, these differences can be pivotal.

The Qinghai test contributes to a growing body of field data reinforcing the potential of BC to lead the next wave of solar efficiency gains, pushing beyond incremental improvements and into a new era of performance.